The connections of the inferior colliculus and the organization of the brainstem auditory system in the greater horseshoe bat (Rhinolophus ferrumequinum).

Hermann Schweizer

doi:10.1002/cne.902010104

Abstract

The connections of the inferior colliculus, the mammalian mid-brain auditory center, were determined in the greater horseshoe bat (Rhinolophus ferrumequinum), using the horseradish peroxidase method. In order to localize the auditory centers of this bat, brains were investigated with the aid of cell and fiber-stained material. The results show that most auditory centers are highly developed in this echolocating bat. However, the organization of the central auditory system does not generally differ from the mammalian scheme. This holds also for the organization of the superior olivary complex where a well-developed medial superior olivary nucleus was found. In addition to the ventral and dorsal nuclei of the lateral lemniscus a third well-developed nucleus has been defined which projects ipsilaterally to the inferior colliculus and which was called the intermediate nucleus of the lateral leminiscus. All nuclei of the central auditory pathway project ipsi-, contra-, or bilaterally to the central nucleus of the inferior colliculus with the exception of the medial nucleus of the trapezoid body and the medial geniculate body. The tonotopic organization of these projections and their possible functions are discussed in context with neurophysiological investigations.

Highlights

The results show that most auditory centers are highly developed in this echolocating bat
This paper presents data on the structure of the lower auditory centers and the connections of the inferior colliculus of the greater horseshoe bat, Rhinolophus ferrumequinum, and tries to clarify the question of whether there are fundamental differences in the anatomical organization of the central auditory system of echolocating bats in comparison to that of other mammals
Three major findings on the anatomical organization of the auditory system of the greater horseshoe bat have to be emphasized and will be discussed in more detail in this paper: (1)Medial to the lateral superior olivary nucleus (LSO) a cell group exists which seems to be homologous to the medial superior olivary nucleus (MSO) in other mammals, judging from the projection pattern to the IC; (2) there is a large nucleus between the VNLL and the DNLL which projects to the IC and which was called the intermediate nucleus of the lateral lemniscus (INLL); and (3) the tonotopical arrangement of the projections to the ICC shows the overrepresentation of the high-frequency regions in the auditory system

Summary

Introduction

The results show that most auditory centers are highly developed in this echolocating bat. The organization of the central auditory system does not generally differ from the mammalian scheme. Insectivorous bats are mammals that hunt at night with the help of a n active sonar system They emit ultrasonic calls and extract from the returning echoes information about their environment and their prey with the aid of a highly developed auditory system. Poljak concluded that the organization of the central auditory pathway in these bats does not differ significantly from that of other mammals. His studies of fiber connections were done only with myelin-stained material

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